A central issue in developmental neurobiology is understanding the molecular regulatory networks that control neuronal specification, differentiation and maintenance. A number of homeodomain transcription factors have been shown to be key molecular players in the control of neurogenesis. We have demonstrated that the POU homeodomain transcription factors Brn3a and Brn3b play essential roles during sensorineural development. The Barhl1 homeodomain factor is selectively expressed in the inner ear sensorineural epithelium as well as in the central nervous system (CNS), suggesting that it may also play an important role in sensorineural development and CNS development. This proposal aims to address the fundamental mechanisms governing vertebrate neural development, using homeodomain-containing transcription factors as models for our analyses. The studies outlined in this proposal are designed to provide integrated approaches for understanding the molecular and cellular mechanisms by which homeodomain transcription factors control sensonneural development and CNS development. Three specific aims will be pursued. First, various developmental defects will be analyzed in the spiral, vestibular and geniculate ganglia of single and compound Brn3a and Brn3b knockout mice. The goal is to understand in vivo the developmental and cellular processes that Brn3a and/or Brn3b regulate during development of the facial-stato-acoustic ganglion. Second, to identify Brn3a binding proteins that may modulate Brn3a selection and activation of target genes during sensorineural development, novel Brn3a protein partners will be isolated using a yeast two-hybrid screening approach. Their functional relevance will be investigated by studying their effects on DNA-binding, transcriptional property and subcellular localization of Brn3a, and by examining their developmental expression patterns. Third, to understand in vivo the roles that Barhl1 plays during vertebrate inner ear and CNS development, we will generate and characterize Barhl1 knockout mice and analyze the biological consequences of forced expression of Barhl1 in the chick cerebellum. Together, these proposed studies will provide important insights into the in vivo biological activities of Brn3 and Barhl1 transcription factors as well as general insights into the molecular mechanisms that govern mammalian neurogenesis and neurological disorders.